A Laser Photolysis Shock Tube Study of the Reaction of OH with NH3

  • John D. Mertens
  • Margaret S. Wooldridge
  • Ronald K. Hanson
Conference paper


The reaction of OH with NH3 has been studied in reflected shock wave experiments using laser photolysis of NH3/N2O/Ar mixtures. Quantitative time-histories of the OH(X 2Πi) radical were measured behind the shock waves using cw, narrow-line width laser absorption at 307 nm. OH was generated using post-shock laser photolysis of ammonia followed by the reaction of atomic hydrogen with N2O:
$$N{H_3} + \hbar \nu (193nm) \to N{H_2} + H{N_2}O + H \to {N_2} + OH$$
Ammonia photolysis yields were confirmed by quantitative measurements of the NH2 radical using cw, narrow-linewidth laser absorption at 597 nm. Initial mixture concentrations and test conditions were chosen such that photolysis and pyrolysis of N2O and pyrolysis of NH3 do not play a significant role in OH reaction kinetics. Following the production of OH by reaction (1), OH-removal is dominated by reaction (2):
$$N{H_3} + OH \to N{H_2} + {H_2}O$$

NH3 + OH → NH2 + H2O

This makes it possible to determine the second-order rate coefficient of reaction (2) by adjusting the value of k 2 in a detailed reaction mechanism until calculated OH concentrations fit the measured OH profiles. A least-squares two-parameter fit of the results is given by:
$${k_2} = 1.1 \times {10^{14}}\exp ( - 4600/T,K)c{m^3}mol{e^{ - 1}}{s^{ - 1}}(f = 0.65,F = 1.45)T = 1240 - 1480K,$$

where f and F are the minimum and maximum rate coefficient factors. The activation energy of the above expression is a parameter determined by the least-squares fitting procedure, and is subject to large uncertainties.

This result is in excellent agreement with the expression recommended by Cohen and Westberg (1991) in their review of reaction (2):
$${k_2} = 5.0 \times {10^7}{T^{1.6}}\exp ( - 480/T,K)c{m^3}mol{e^{ - 1}}{s^{ - 1}}T = 225 - 3000K.$$

Key words

Shock Tube Reaction Kinetics Ammonia Hydroxyl Laser absorption 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Cohen N, Westberg KR (1991) Chemical kinetic data sheets for high temperature chemical reactions. J. Phys. Chem. Ref. Data. 20: 1211–1311CrossRefADSGoogle Scholar
  2. Davidson DF, Chang AY, Kohse-Höinghaus K, Hanson RK (1989) High temperature absorption coefficients of O2, NH3, and H2O for broadband ArF excimer laser radiation. J. Quant. Spectrosc. Radiat. Transfer 42: 267–278CrossRefADSGoogle Scholar
  3. Hanson RK, Salimian S (1984) Survey of rate constants in the N/H/O system. Ch. 6 Combustion Chemistry, Gardiner WC (ed) Springer-Verlag New York: 361–421Google Scholar
  4. Kee RJ, Miller JA, Jefferson TH (1980) Chemkin: A general-purpose problem-independent, transportable, Fortran chemical kinetics code package, Sandia National Laboratory Report No. SAND80-8003Google Scholar
  5. Kee RJ, Rupley FM, Miller J A (1991) The Chemkin thermodynamic data base, Sandia National Laboratory Report No. SAND87-8215BGoogle Scholar
  6. Kohse-Höinghaus K, Davidson DF, Chang AY, Hanson RK (1989) Quantitative NH2 shock tube laser-absorption experiments. J. Quant. Spectrosc. Radiat. Transfer 42: 1–17CrossRefADSGoogle Scholar
  7. Lutz AE, Kee RJ, Miller J A (1988) Senkin: A Fortran program for predicting homogeneous gas phase chemical kinetics with sensitivity analysis. Sandia National Laboratory Report No. SAND87-8248Google Scholar
  8. Marshall P, Fontijn A, Melius CF (1987) High-temperature photochemistry and BAC- MP4 studies of the reaction between ground-state H atoms and N2O. J. Chem. Phys. 86: 5540–5549CrossRefADSGoogle Scholar
  9. Mertens JD, Chang AY, Hanson RK, Bowman CT (1991a) A shock tube study of the reactions of NH with NO1, O2, and O. Intl. J. Chem. Kinetics 23: 173–196CrossRefGoogle Scholar
  10. Mertens JD, Kohse-Höinghaus K, Hanson RK, Bowman CT (1991b) A shock tube study of H + HNCO→NH2+CO. Intl. J. Chem. Kinetics 23: 655–668CrossRefGoogle Scholar
  11. Meyer SL (1975) Data analysis for science and engineering. John Wiley and Sons, Inc. New YorkGoogle Scholar
  12. Rea EC, Salimian S, Hanson RK (1984) Rapid-tuning frequency-doubled ring dye laser for high resolution absorption spectroscopy in shock-heated gases. Appl. Opt. 23: 1691–1694CrossRefADSGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1995

Authors and Affiliations

  • John D. Mertens
    • 1
  • Margaret S. Wooldridge
    • 2
  • Ronald K. Hanson
    • 2
  1. 1.Department of EngineeringTrinity CollegeHartfordUSA
  2. 2.High Temperature Gasdynamics Laboratory, Department of Mechanical EngineeringStanford UniversityStanfordUSA

Personalised recommendations